This invention relates to the construction industry, and more particularly, to roof flashings of the type which reinforce the interface between a wall and a roof edge to provide a waterproof and weather resistant seal along the edge of the roof.
Roof flashing is conventionally used to provide a waterproof and weather resistant seal about the periphery of the roof edge, as well as around the pipes and vent stacks. The flashing is usually made of sheet metal, flexible molded rubber or other synthetic material formed in an appropriate shape to seal the periphery of the projecting members, and is normally made to extend slightly above the level of the roof, to limit the infiltration of moisture into the building. In flat roofs, the roof edge is conventionally sealed using the so-called cant strips. Generally, roof systems used on most building structures, and particularly flat-roof buildings, require some type of blocking to provide a base for the attachment of roofing components, such as nailed down cant strips, that are used for parapet walls, skylight curbs or other construction details forming substantially 90 degree angles with a roof decking.
Typically, cant strips have been made of wood or a wood fiber material and have had triangular shaped cross sections thereby providing a 45-degree angle instead of the 90-degree angle that is created between a parapet wall and the roof. However, the triangular cross sectioned cant strips create a stressful angle for the membranes to follow as the transition from the horizontal roofing deck to the triangular cross sectioned cant strip still requires a transition angle of 45 degrees and this often is too much angle for the roofing membrane to handle over time. In particular, asphalt membranes still have a tendency to crack and split at the 45-degree angle between the horizontal decking surface and the cant strip surface.
Second, as the cant strip is made of wood or wood fiber material, they can absorb water and decompose if small cracks in the membrane go undetected and water penetrates to the cant strip surface. The cant strip can hold this moisture and subsequently promote dry rot of wood decking, sheathing or structural members. Third, the cant strip positioning is labor intensive, requiring four steps of cutting material and securing to the parapet wall. Once the cant strip is installed, a counter flashing should be cut into the wall and overlap the top edge of the roof membrane, secured to the parapet wall.
In flat roofs, the danger of the wind force lifting the roof edge and of standing water seeping in the cracks between the cant strips and the parapet wall remains high. It is critical to provide a long lasting, water tight seal of any gap that exists between the flashing and the projecting member. Commonly, such gaps are sealed by caulking with resilient materials, such as silicon. However, caulking can only be used in the locations where a narrow gap exists. Moreover, the roof flashing and stack members may move relative to each other due to weather conditions, which causes cracks in the caulk material, thus creating additional area for moisture penetration. Further, caulking can be difficult to work with, can have a limited effective lifetime, and can be expensive. Moreover, its installation is labor-intensive.
The present invention contemplates elimination of drawbacks associated with conventional roof systems and provision of a roof flashing assembly that can be used at the interface of a building roof and a wall, along the roof edge to securely seal the area between the building wall and the roof structure.